Focusing device for motion picture projectors



March 1, 1932. J D M 1,847,856 FOCUSING DEVICE FOR MOTION PICTURE PROJECTORS Filed Dec. 15. 192'? 2 Sheets-Sheet l Ilia-.1-

WITNES 5E5 INVICINTOR;

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BY I 9"" '/W ATTORNEY.

March 1, 1932. J. F. ADAMS 1,847,856

FOCUSING DEVICE FOR MOTION PICTURE PROJECTORS Filed Dec. 13. 1927 2 Sheets-Sheet 2 I N VENTOR:

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, Patented Mar. 1,1932

ES PATENT OFF-ICE a l I q JOHN FRANCIS ADAMS, OF PHILADELPHIL' PENNSYLVANIA, ASSIGNOB TO SENTBY SAFETY common conromrron, or rmmnrmmm, runnsnvmm, A conrona- 'non' or DELAWARE I rocusme DEVICE r03 MOTION ,PIc'rU-BE mmc s Application filed December 13-, 1827. Serial No. 289,621.

My invention relates tomotion picture projectors and has special reference to means for adjusting the lens holderthereof.

Many projectors now in use are focused by means of a gear and rack and the lens holders are then clamped in selected-positions. The

diificulty with this arrangement lies 'inthe fact that adjustments must be made often and accurately in order to produce proper projection as the lens must be readjusted whenever a different thickness of film is run through the projector and whenever the film a is printed on both sides, as in colored films.

. As there is always some backlash between 5 the pinion ,andrack, it is difiicult to quickly and accuratelyadjust the lens holder and,

unless securely clamped in adjusted position, I

it will work out of focus due .to the vibration of the projector. adjusted whenever the lens is cleaned, the position of the reflector in the lamp housing changed, a film of a different thickness used, and whenever the lens is jarred out of adjustment by the vibration of theprojector. Thus the operator is forced to perform duties which require constant attention and it is the vobject of this invention to provide a device which will enable him to adjust the lens holder quickly and accurately and which will secure same against displacementdueto the vibration of the projector. i I

Other objects of the invention are to provide a device whichpermits a much finer ad-' .justment, is more easily operated, has fewer parts, and is so designed that no alteration to the projector is necessary in order to install same thereon.

In the drawings: Figure 1 is a perspective view of a motion picture projector upon which my improved adjusting device has been installed.

Figure 2 -is a fragmentary sectional View through a portion of the projector, as indi: cated by the line 2-2-on Figure 1, showing the adjusting device in operative position. Figure 3 is a front view of the front plate of the projector shown in Figure 1, showing the lens holder and adjusting device in place, and

The lens holder must be;

' very-long lens hol er 6 a considerable distance from -Figure 4 a bottom sectional plan view thereof, taken on lineA- t on Figure 3.

The-projector illustrated-in the drawings has a front plate 5 .which normally supports a lensv holder (5 by means of a pair of guide rods 7 upon which lens holder 6 is slidable and which are secured in front plate 5'by set screws 8. In installing myimpro'ved adjusting device upon a projector, I remove one guide rod 7 and substitute therefor a tlieaded rod 9 which is preferably provided with a V- shaped groove 10 near its inner end into which the point of set'screw 8 may enter for fixing rod 9 in-place. A coiled spring 11 encircles rod 9 between front plate 5 andlens holder 6 and tends to slide the lens holder on rods 7 and 9 away from front plate 5.

The outer end of 'od 9 provided with a fine thread 12 upon hich a nut 13 is threaded into engagement with lens holder 6; ,nut 13 being provided with a counterbore 14 so that lens holder 6' does not slide over threads 12 when it is in its forwardmost position. In order to prevent nut 13 from being unintentionally removed' from rod 9, the outer end of the rod is bored and tapped to receive a screw 15 which may have a large head or be provided with a washer 16 which 'is slightly larger than the threaded portion of 1 posed on rod 9 between lens holder 6 and washer 16. In both cases, nut 13 is adapted to move lens holder 6 agahist both the action of spring 11 and the force ofgravity.

.When the projector upon which the device is to be installedis in operationfin a theatre, 1t is necessary 't position front plate 5 in order to focus the pictizv upon the screen. Instead 'of providing long spring in place of spring '11, one or.

more collars 17 are provided which are disposed between lens holder 6 and spring 11 so that the same adjusting device may be used on projectors which are to be focused to both long and short distances.

When a portion. of the film of a different thickness or a colored section passes the projection aperture, the operator simply has to turn nut 13 in one direction or the other -to bring the picture into the proper focus upon the screen, in which position the lens holder will remain-due to the action of spring 11 and nut 13 which cannot be affected by the vibration of the projector. It is also to be noted'that this arrangement allows a much finer adjustment and that the adjustment can be made in considerably less time than by the customary means now in use.

While I have described one manner of carrying'my invention into eifect and have shown the device applied to one type of pro-,

jector, it is to be understood that it may be applied to other types of projectors and to cameras or the like and that modifications of the device may be made Without departing fromthe spirit of the invention, as set forth in the foregoing specification and as hereinafter claimed.

I claim 1. Means for horizontally adjusting the lens holder of a motion picture machine relative to its support, comprising a pair of rods fixed in the support, said lens holder being slidably mounted on said rods, one of said rods having a threadedportion on its outer end, a nut on said threaded portion, the

otherrod being unthreaded, and a spiral spring surrounding said threaded rod between said lens holder and said support for firg ng' said holder against said nut wherej 7 said holder moves longitudinally and without any lateral displacement upon, the adjustment of said nut.

2. Means for horizontally adjusting the lens holder of a motion picture machine relative to its support, comprising a pair of rods fixed in the support, said lens holder having sleeves whereby it is slidably mounted on said rods,- one of said rods having a threaded portion on its outer end, a nut on said threaded portion, and a spiral spring surrounding said threaded rod between'said lens holder and the sleeve slidably mounted on said rod for urging said holder against said nut whereby said holder will move forward or rearward without lateral displacement upon the adjustment of said nut.

In testimony whereof I have signed my name to this specification.

JOHN FRANCIS ADAMS. 

